Tag Archives: mtDNA

In this week’s parasha, Va’etchanan, God cautions His people about intermarriage (Deuteronomy 7:3-4). Although the Torah is speaking specifically about intermarrying with the Canaanite nations, the verses have always been understood as prohibiting intermarriage with any and all other nations. This is especially true because the Torah goes on to say that intermarrying will lead to the children being led astray and being turned to idolatrous ways. In those days, the Canaanites were not the only idolaters, of course—just about everyone was an idol-worshipper—so all intermarriage was forbidden. The Torah phrases the prohibition in an interesting way:

You shall not intermarry with them; you shall not give your daughter to his son, and you shall not take his daughter for your son, for they will turn away your son from following Me, and they will worship the gods of others…

While the Torah makes it clear that one must not marry their son to a gentile woman, or their daughter to a gentile man, it goes on to only mention that the son will be turned away from God, not the daughter. The Sages explain that women tend to be of greater faith than me, and as the primary builders of the home, it is the women who set the spiritual tone of the family. A faithful Jewish man who marries a non-Jewish woman will, sooner or later, be led astray. Such was the case with a great many Jewish men following the Babylonian Exile, and when they finally returned to Israel, they admitted (Ezra 10:2-3):

We have broken faith with our God, and have married foreign women of the peoples of the land; yet now there is hope for Israel concerning this thing. Now therefore let us make a covenant with our God to put away all the wives, and such as are born of them, according to the counsel of Hashem, and of those that tremble at the commandment of our God; and let it be done according to the law.

“Ezra reading the Law in the hearing of the people” by Gustave Doré

From all of the above, the Sages conclude that Judaism passes on maternally. Scripture makes it clear that only the non-Jewish mother will turn a Jewish man astray, and as we learn from Ezra, only those born to “foreign women” are not part of the Covenant. Aside from this, there are a number of other practical and spiritual reasons why Judaism must be matrilineal.

Since the mother is the one actually giving birth to the child, it is pretty much clear every single time who the child’s mother is. The same cannot be said of the father. Throughout history, when raping and pillaging was unfortunately very common, and there were no paternity tests, only the mother’s status as parent was evident. This may be why the ancient Greeks and Romans tended to be matrilineal as well.

Shaye J.D. Cohen points out (see chapter 9 of The Beginnings of Jewishness) that in Athens, only the offspring of an Athenian man and an Athenian woman could have Athenian citizenship, a law introduced by Pericles around 451 BCE. If an Athenian man married a foreign woman, the children would not be Athenians. Later, the Romans similarly held that only two Roman citizens can have a child who was a Roman citizen, and if a Roman married a foreigner or someone of a lower social class, the status or identity of the child would be that of the mother.

While these rules make sense from a logical perspective, they also recognize the profound connection that a child and mother have—far superior to that of child and father. And this ties into the deeper biological, and spiritual, reasons for why Judaism is matrilineal.

The Genetics of Motherhood

When it comes to the genes and traits of children, people tend to think that they are a 50-50 mix of mother and father. We learn in school how 23 chromosomes from the father (carried by sperm cells) meet 23 chromosomes from the mother (in the egg cell) to produce a new child. We are made to believe that even if the child may look more like one parent, they are nonetheless perfectly half-half. This is completely untrue.

A karyotype showing 23 pairs of chromosomes. (Credit: National Human Genome Research Institute)

First of all, when it comes to boys, the Y chromosome of the father is far smaller and carries significantly less genes than the mother’s X chromosome. Girls do have half of their father’s and half of their mother’s genes (receiving an X from each, along with the other 22 chromosomes). However, this only refers to nuclear DNA. The cell has other forms of heritable genetic material, too, most notably in mitochondria.

The mitochondrion is one of the most vital components of any cell, and provides the bulk of a cell’s energy. The main reason that you breathe is to provide oxygen for mitochondria. They are involved in countless processes, including calcium storage, cell signalling and communication, metabolism, hormone production, the breakdown of wastes (such as toxic ammonia in the liver), and apoptosis, or cellular death. A single cell could have over a thousand mitochondria.

Mitochondria under a microscope.

These mitochondria have their very own DNA, carrying hundreds of additional genes. This DNA, called mtDNA, is passed down strictly from mother to child. A father’s mitochondria play no role. In fact, because of this, geneticists are able to trace a person’s maternal lineage fairly accurately thousands of years into the past by analyzing mtDNA. (My own mtDNA—haplogroup U6a—dates back to a woman who lived in North Africa about 1000 generations ago!)

There are multiple other cellular components that are passed down almost entirely from mother to child. Because the sperm essentially donates only its nucleus (with its chromosomes) to the egg, it is the egg cell itself that begins to divide in producing an embryo. Thus, the bulk of a person’s cellular structure comes from their mother, too. Back in university, I had one biology professor who estimated that inheritance is not 50-50, but more like 80-20. From a scientific perspective, we are far, far more like our mothers.

This is one reason why mothers have such a deep and profound connection to their child. Amazingly, scientists have recently discovered that when a woman is pregnant, DNA (and whole cells) from the child actually goes into the bloodstream and ends up in the mother’s brain! Fetal cells have also been found in lungs, muscles, and heart tissue of mothers. A mother will literally carry the DNA of her children in her body for the rest of her life.

Just as children are physically more connected with their mothers so, too, are they more spiritually connected to their mothers. (After all, one of Judaism’s central principles is that the dynamics of this physical world are only a reflection of the spiritual realms.) And this is yet another key reason why Judaism is, and must be, matrilineal.

What About Conversion?

The genetics perspective brings up an important question: what about converts? A person who converts to Judaism is, of course, a full-fledged Jew. But their DNA hasn’t changed! It goes without saying that Judaism is not genetic, and the discussion of genetics above is meant to only be an analogy for spiritual processes.

Having said that, we have an opportunity here to bust another common myth: that a person’s DNA is unchanging. People are often taught that whatever DNA they are born with, they are stuck with. If they have a defective gene for a particular condition, then they will definitely develop that condition. Today we know that this, too, is not entirely correct.

As discussed before in detail, our body has epigenetic machinery which allows gene expression to be controlled. Just because a person has a certain gene does not mean that the gene will be operational. It can certainly be “shut off”. While it was once thought that our lifestyle choices have no impact on our genes or epigenetics, new research continues to show that the choices we make have a tremendous effect on our genes. We’ve known for a long time that things like diet and physical activity impact gene expression, and now we even have evidence that prayer and meditation affects our genes.

Therefore, a person who sincerely converts to Judaism, and begins to live a Jewish lifestyle, eat like a Jew, think like a Jew, and pray like a Jew, will very likely experience changes on the genetic (or epigenetic) level as well. And these epigenetic changes are hereditary.

This is yet another reason why it is so important to convert to Judaism properly. Converting means not only converting in name, but becoming Torah-observant and living a Jewish life. Otherwise, what’s the point of the conversion? This is precisely why Orthodox conversions tends to be so difficult and time-consuming. The rabbis want to ensure (as much as possible) that the person is serious about becoming a Jew, and will actually live as one.

The process is far from perfect, and sometimes they do make it too difficult and tedious. We have addressed this in the past as well. Some point out that it was never so difficult to convert in past centuries. This is true, as the Talmud (Yevamot 47b) explains the procedure thus:

Once healed [from circumcision], we immerse him immediately; and two scholars stand above him, and teach him a few easy commandments and a few difficult commandments. Once he has immersed and come up from immersion, he is part of Israel for all matters. If the convert is a woman, women sit her in the water up to her neck and two scholars stand outside, and teach her a few easy commandments and a few difficult commandments.

That’s all it took back in those days. A person was just taught a few introductory mitzvot while already immersed part way in a mikveh. They would pick up the rest when going on to live as Jews and marry into Jewish families. Even in the time of the Rambam (Rabbi Moshe ben Maimon, 1135-1204) hundreds of years later, he codifies this exact procedure as law (Mishneh Torah, Issurei Biah 14:6). Yet, in those days just about everyone was religious (whether Jewish or not). This isn’t the case in today’s secular society. A person who converts to Judaism wouldn’t necessarily learn how to be a Jew by simply marrying into a Jewish family. It is necessary to carefully teach them everything beforehand.

It is just as necessary to determine their real intentions, and affirm their absolute sincerity. In a world where people change their identities faster than they change their socks, it isn’t surprising that Orthodox rabbis take conversion very seriously and are extremely stringent about it. It is important to keep this in mind as we continue to hear about intermarriage and the “who is a Jew?” debate in the mainstream media.